As the size of the portable electronic apparatuses involving mobile telephones and the PHSs (personal handyphone systems) becomes smaller, a demand has been raised for reducing the weight, the thickness and the size for a light emitting device used therefor. In particular, there has been a recent demand for obtaining a thin, low-height, chip light emitting device.
The chip light emitting device of this kind, that is made small and thin, includes a substrate 1, as shown in FIG. 5(a). The substrate 1 is formed with terminal electrodes 2, 3 at opposite ends, one of which electrodes 2 has a portion mounted with a light emitting diode (hereinafter referred to as "LED") chip 4 through die-bonding. The LED chip 4 has a bottom electrode directly connected with the terminal electrode 2 and a top electrode wire-bonded to the other terminal electrode 3 through a gold wire 7, thus providing respective electrical connections between the LED chip 4 and the terminal electrodes 2, 3.
The LED chip 4 has, for example, an n-type semiconductor layer 41 and a p-type semiconductor layer 42 which are formed of GaAs or GaP to have a pn junction plane (or light emitting layer) 43 defined therebetween. The LED chip 4 has opposite surfaces respectively provided with end electrodes 44, 45. The substrate 1 encapsulated at its main surface by a transparent or milk-white epoxy resin so as to cover the LED chip 4, the gold wire 7, etc. for their protections.
The LED chip 4 has its size, i.e. the depth A and the width B respective of which are in dimension of approximately 0.24-0.35 mm. The chip 4 also has its thickness T in dimension equivalent to the depth and the width, i.e. made almost in a cubic form. These depth A and the width B are generally determined to an equal length to each other, in order to facilitate wire-bonding with using a gold as well as provide evenness in brightness of the light to be emitted. Moreover, if the one or both of the dimensions of the depth and the width is taken smaller than the value stated above, the resulting area of the pn junction plane 43 is also decreased. In such a case, however, if an amount of current supply to the reduced area of the pn junction plane is increased in order to increase the amount of light emission from the limited light emitting area of the chip, there is a fear that the semiconductor layers undergo serious injury or accelerated deterioration. It is therefore difficult, in reducing the area of the pn junction plane 43, to provide a required amount of light emission. In the meanwhile, if the thickness T is reduced, the wafer before dicing is liable to warp or distort, making it difficult to provide a uniform quality to the LED chip. Accordingly, the size reduction of the LED chip is limited in thickness to the aforementioned cubic form.
As stated above, it is practically difficult for the conventional chip light emitting device to make further compact, because its LED chip is now on the lower limit of size due to the necessity of providing a required area to the light emitting layer thereof. However, as the mobile telephone or the PHS becomes more compact, there is a further demand for reducing the size of electronic components or parts. In particular, the thinning of thickness is now demanded especially for the chip light emitting device.